Compass
A live compass using your phone's sensors to show which way is north, with the difference between magnetic and true north made explicit.
Location for true north
Declination is computed in your browser from the World Magnetic Model. Nothing is sent anywhere, and you can type a position instead of sharing one.
A magnetic compass does not point north
The angle between magnetic north and true north is called declination, and it is not a small correction. It runs about 16 degrees east in Seattle, 13 degrees west in New York, 25 in parts of Alaska, and passes 90 near the magnetic poles. A bearing walked without correcting for it drifts roughly 280 metres per kilometre at 16 degrees — over ten kilometres that is nearly three kilometres off line, which is a different valley.
Declination also changes with time, which is why the figure printed in the margin of an old map misleads. The field drifts by several minutes of arc a year, so a chart from the 1990s can be a degree or two out today. That drift is why the World Magnetic Model is reissued every five years and why this page carries the 2025 coefficients along with their rate-of-change terms.
The model here is the published WMM2025 set rather than an approximation, and the implementation reproduces all twelve of NOAA's official test values to within five thousandths of a degree. That check is the whole reason to trust it — a spherical harmonic model with a subtle error still returns confident, plausible-looking numbers, and there is no way to spot the difference by eye. What it cannot see is local iron: the steel in your car, a magnet in a phone case, or a belt buckle will each move a needle further than the difference between a good model and a mediocre one.
How to use
- Allow motion and orientation access when prompted.
- Share your location, or type coordinates, to switch from magnetic to true north.
- Hold the phone flat and level, and calibrate with a figure-of-eight if it wanders.
- Move away from metal and electronics before trusting it.
Frequently asked questions
Does this compass show true north or magnetic north?
Both, and it says which. Without a location it shows magnetic north, because that is all a magnetometer knows. Give it a position — shared or typed — and it computes magnetic declination from the World Magnetic Model 2025 in your browser and switches to true north, labelling the reading so you always know which one you are looking at.
How large is the declination correction?
Larger than most people expect. It runs about 16 degrees east in Seattle, 13 degrees west in New York, 25 in parts of Alaska, and passes 90 near the magnetic poles. At 16 degrees an uncorrected bearing drifts roughly 280 metres for every kilometre walked, so over ten kilometres you are nearly three kilometres off line.
Is my location sent anywhere to work out declination?
No. The World Magnetic Model coefficients are built into the page and the calculation runs entirely in your browser, so no position ever leaves the device. That is also why you can type a latitude and longitude instead of sharing your real one, and why it still works with no signal once the page has loaded.
How accurate is the declination figure?
The model is the published WMM2025 coefficient set rather than an approximation, and this implementation reproduces all twelve of NOAA official test values to within five thousandths of a degree. What it excludes is local crustal magnetism, which can add whole degrees in some places, and magnetic storms. Your phone sensor is the larger error by far.
Why is declination different from the number printed on my map?
Probably because the map is old. The magnetic field drifts by several minutes of arc a year, which is why the World Magnetic Model is reissued every five years and why this page carries rate-of-change terms alongside the coefficients. A chart from the 1990s can easily be a degree or two out today.
What is the difference between magnetic and true north?
Magnetic north is where the compass points; true north is the geographic pole. The angle between them is magnetic declination, and it varies by location from negligible to well over twenty degrees. Navigating with a map by an uncorrected magnetic bearing puts you increasingly wrong over distance.
Why does the reading jump around?
Because a phone's magnetometer is small, sensitive and easily disturbed. Steel structures, speakers, magnetic phone cases and car bodies all distort the field, and so does the phone's own electronics. Calibrating with a figure-of-eight motion helps, and moving away from metal helps more.
Is a phone compass accurate enough for navigation?
For general orientation, yes. For anything where being wrong matters — backcountry route-finding, marine navigation — a baseplate compass is more reliable, does not depend on a battery, and cannot be thrown off by a software issue. Carrying both is the usual advice.
Does the compass work without a signal?
Yes. The magnetometer is a physical sensor and needs no network. What does need a signal, or a stored location, is the declination correction, since it depends on knowing where you are.
Does the magnetic pole move?
Continuously, and faster than it used to — the north magnetic pole has been migrating across the Arctic at a considerable rate in recent decades. This is why declination values are revised on a regular cycle and why an old map's stated declination should not be trusted.
Why does my phone ask me to wave it in a figure of eight?
To sample the magnetic field from multiple orientations so it can work out and subtract the distortion caused by the phone itself and its surroundings. It looks silly and genuinely improves the reading.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.